Photolabile Molecules Research Articles

Localized Crystallization of Calcium Phosphates by Light-Induced Processes.

Medical treatment options for bones and teeth can be significantly enhanced by taking control over the crystallization of biomaterials like hydroxyapatite in the healing process. Light-induced techniques are particularly interesting for this approach as they offer tremendous accuracy in spatial resolution. However, in the field of calcium phosphates, light-induced crystallization has not been investigated so far. Here, proof of principle is established to successfully induce carbonate-hydroxyapatite precipitation by light irradiation. Phosphoric acid is released by a photolabile molecule exclusively after irradiation, combining with calcium ions to form a calcium phosphate in the crystallization medium. 4-Nitrophenylphosphate (4NPP) is established as the photolabile molecule and the system is optimized and fully characterized. A calcium phosphate is crystallized exclusively by irradiation in aqueous solution and identified as carbonate apatite. Control over the localization and stabilization of the carbonate apatite is achieved by a pulsed laser, triggering precipitation in calcium and 4NPP-containing gel matrices. The results of this communication open up a wide range of new opportunities, both in the field of chemistry for more sophisticated reaction control in localized crystallization processes and in the field of medicine for enhanced treatment of calcium phosphate containing biomaterials.

1,4-Naphthoquinone Derivative as Efficient Photolabile Molecule: Concise Synthesis and Photorelease of Various Functional Compounds

AbstractWe report on a series of 1,4-naphthoquinone (NQ)-based photolabile molecules, including various functional compounds to be released under light irradiation. They were efficiently prepared from a common precursor for a photoremovable masking group, by attaching different functional compounds such as alcohols, amines, and acids by a concise synthetic method. Synthesis of the common precursor was optimized for two-step reactions and also for a one-pot reaction involving a 1,4-addition and successive aldol reaction from NQ. The functional compounds, such as alcohols, amines and carboxylic, phosphoric, and sulfonic acids, were masked with the NQ-based precursor and were successfully released by irradiation with UV light (λ = 360 nm) in high yields (>90%).

Xanthoepocin, a photolabile antibiotic of Penicillium ochrochloron CBS\xa0123823 with high activity against multiresistant gram-positive bacteria

BackgroundWith the steady increase of antibiotic resistance, several strategies have been proposed in the scientific community to overcome the crisis. One of many successful strategies is the re-evaluation of known compounds, which have been early discarded out of the pipeline, with state-of-the-art know-how. Xanthoepocin, a polyketide widespread among the genus Penicillium with an interesting bioactivity spectrum against gram-positive bacteria, is such a discarded antibiotic. The purpose of this work was to (i) isolate larger quantities of this metabolite and chemically re-evaluate it with modern technology, (ii) to explore which factors lead to xanthoepocin biosynthesis in P. ochrochloron, and (iii) to test if it is beside its known activity against methicillin-resistant Staphylococcus aureus (MRSA), also active against linezolid and vancomycin-resistant Enterococcus faecium (LVRE)—a very problematic resistant bacterium which is currently on the rise.ResultsIn this work, we developed several new protocols to isolate, extract, and quantify xanthoepocin out of bioreactor batch and petri dish-grown mycelium of P. ochrochloron. The (photo)chemical re-evaluation with state-of-the-art techniques revealed that xanthoepocin is a photolabile molecule, which produces singlet oxygen under blue light irradiation. The intracellular xanthoepocin content, which was highest under ammonium-limited conditions, varied considerably with the applied irradiation conditions in petri dish and bioreactor batch cultures. Using light-protecting measures, we achieved MIC values against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), which were up to 5 times lower than previously published. In addition, xanthoepocin was highly active against a clinical isolate of linezolid and vancomycin-resistant Enterococcus faecium (LVRE).ConclusionsThis interdisciplinary work underlines that the re-evaluation of known compounds with state-of-the-art techniques is an important strategy in the combat against multiresistant bacteria and that light is a crucial factor on many levels that needs to receive more attention. With appropriate light protecting measures in the susceptibility tests, xanthoepocin proved to be a powerful antibiotic against MRSA and LVRE. Exploring the light response of other polyketides may be pivotal for re-introducing previously discarded metabolites into the antibiotic pipeline and to identify photosensitizers which might be used for (antimicrobial) photodynamic therapies.

Preparation and Characterization of Indomethacin Supramolecular Systems with β-Cyclodextrin in Order to Estimate Photostability Improvement.

Cyclodextrins have found wide application in contemporary chemistry, pharmacy and medicine. Because of their unique properties, cyclodextrins are constantly used in research on solubility or stability improvement, as well as other physicochemical properties of medicinal substances. Indomethacin (IND) is a photolabile molecule that also attracts the interest of researchers due to its therapeutic potential and the need to overcome its problematic photosensitivity. Supramolecular complexes of indomethacin with β-cyclodextrin (CD) are already known, and they show greater stability compared to complexes with other types of cyclodextrins. So far, however, the sensitivity to light of physical mixtures and inclusion complexes in the solid phase has not been studied, and their various stoichiometries have not yet been investigated. Due to this fact, the aim of the present study is to obtain supramolecular systems (inclusion complexes and physical mixtures) of indomethacin with three different amounts of β-cyclodextrin. Assessment of the photochemical stability of indomethacin-β-cyclodextrin systems in the solid state is performed in order to find the best correlation between IND stability and the amount of CD. Comparative analysis of physicochemical degradation for stoichiometry systems [CD:IND] = [1:1], [0.5:1] and [0.1:1] is performed by using ultraviolet spectroscopy, transmission—FTIR, reflection—ATR-FTIR infrared spectroscopy and DSC calorimetry.

Partially Solvated Dinuclear Ruthenium Compounds Bridged by Quinoxaline-Functionalized Ligands as Ru(II) Photocage Architectures for Low-Energy Light Absorption.

Ruthenium compounds with coordinated photolabile molecules that can be selectively released by irradiation with a visible light source are finding increasing applications in photoactivated chemotherapy (PCT) as photocages. Earlier photocages based on mononuclear Ru(II) compounds lack absorption in the therapeutic window (λ > 600 nm). In previous work, we synthesized the first partially solvated tppz bridged (tppz= 2,3,5,6-tetrakis(pyridin-2-yl)pyrazine) dinuclear Ru(II) complex capable of photoinduced ligand exchange at both metal centers. To further explore the effect of the bridging ligand on Ru(II) photocage design, we used quinoxaline-functionalized bridging ligand platforms to prepare [{RuII(NCCH3)4}2(μ-BL)](PF6)4[BL = dpq, 2,3-di(pyridin-2-yl)quinoxaline (1); BL = dpb, 2,3-di(pyridin-2-yl)benzo[g]quinoxaline (2)]. The compounds are capable of absorbing green light with tails extending beyond 650 nm which can be exploited for applications as PCT agents. Experimental results were additionally verified by DFT calculations. The use of two Ru(II) centers equipped with quinoxaline-based bridging ligands is a promising design strategy for the synthesis of a new family of dinuclear Ru(II) photocage prototypes with the ability to absorb low-energy visible light.

Photodegradation Study of Sertindole by UHPLC-ESI-Q-TOF and Influence of Some Metal Oxide Excipients on the Degradation Process.

The evaluation of the influence of the excipients present in the pharmaceutical formulations on the drug stability is an important part of quality control of medicines. One of the most commonly applied group of excipients are pigments, such as titanium dioxide or various forms of iron oxides, which are well-known photocatalytic agents. Therefore, the photostability of an atypical antipsychotic drug sertindole and the influence of pigments commonly used in the pharmaceutical formulations (FeOOH, Fe2O3, and TiO2) on this process were studied. The quantitative and qualitative analysis of the process was performed with the use of ultra high pressure liquid chromatography with diode array detection (UHPLC-DAD) system coupled with a high resolution hybrid electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer. Sertindole turned out to be a highly photolabile molecule. Overall 18 transformation products were found, mainly formed as a consequence of dechlorination, hydroxylation, and dehydrogenation. In all the experiments, except the TiO2-mediated photocatalysis, the product of chlorine substitution with a hydroxyl group was the major product. The presence of Fe2O3 and TiO2 accelerated the degradation process, while FeOOH served as its inhibitor. The experiments conducted with the use of the pharmaceutical formulations confirmed the catalytic activity of the used excipients. The exploration of the obtained phototransformation profiles with the use of principal component analysis (PCA) revealed that the presence of both iron oxides could influence the qualitative and quantitative aspect of the studied processes. In silico assessment of the properties showed that the transformation products are generally less toxic to rodents, possess lower hERG blocking potential, but could be more mutagenic than the parent molecule.

Janus Gold Nanostars-Mesoporous Silica Nanoparticles for NIR-Light-Triggered Drug Delivery.

Janus gold nanostar-mesoporous silica nanoparticle (AuNSt-MSNP) nanodevices able to release an entrapped payload upon irradiation with near infrared (NIR) light were prepared and characterized. The AuNSt surface was functionalized with a thiolated photolabile molecule (5), whereas the mesoporous silica face was loaded with a model drug (doxorubicin) and capped with proton-responsive benzimidazole-β-cyclodextrin supramolecular gatekeepers (N 1). Upon irradiation with NIR-light, the photolabile compound 5 photodissociated, resulting in the formation of succinic acid, which induced the opening of the gatekeeper and cargo delivery. In the overall mechanism, the gold surface acts as a photochemical transducer capable of transforming the NIR-light input into a chemical messenger (succinic acid) that opens the supramolecular nanovalve. The prepared hybrid nanoparticles were non-cytotoxic to HeLa cells, until they were irradiated with a NIR laser, which led to intracellular doxorubicin release and hyperthermia. This induced a remarkable reduction in HeLa cells viability.

Photoactivated Spatiotemporally-Responsive Nanosensors of in Vivo Protease Activity.

Proteases play diverse and important roles in physiology and disease, including influencing critical processes in development, immune responses, and malignancies. Both the abundance and activity of these enzymes are tightly regulated and highly contextual; thus, in order to elucidate their specific impact on disease progression, better tools are needed to precisely monitor in situ protease activity. Current strategies for detecting protease activity are focused on functionalizing synthetic peptide substrates with reporters that emit detection signals following peptide cleavage. However, these activity-based probes lack the capacity to be turned on at sites of interest and, therefore, are subject to off-target activation. Here we report a strategy that uses light to precisely control both the location and time of activity-based sensing. We develop photocaged activity-based sensors by conjugating photolabile molecules directly onto peptide substrates, thereby blocking protease cleavage by steric hindrance. At sites of disease, exposure to ultraviolet light unveils the nanosensors to allow proteases to cleave and release a reporter fragment that can be detected remotely. We apply this spatiotemporally controlled system to probe secreted protease activity in vitro and tumor protease activity in vivo. In vitro, we demonstrate the ability to dynamically and spatially measure metalloproteinase activity in a 3D model of colorectal cancer. In vivo, veiled nanosensors are selectively activated at the primary tumor site in colorectal cancer xenografts to capture the tumor microenvironment-enriched protease activity. The ability to remotely control activity-based sensors may offer a valuable complement to existing tools for measuring biological activity.

Quantification of Unimolecular Photoreaction Kinetics: Determination of Quantum Yields and Development of Actinometers—The Photodegradation Case of Cardiovascular Drug Nisoldipine

The lack of integrated rate-laws for photoreactions has led to carry out the treatment of drugs photodegradation kinetic data using the classical zeroth-, first-, and second-order kinetics that were originally developed for thermal reactions. The recent developments of Φ-order kinetic models has opened new perspectives in the treatment of photoreaction kinetics of systems involving a photolabile molecule (A) transforming into a photochemically and thermally stable product (B), that is, the AB(1Φ) photoreaction systems. Within this framework, the kinetics of cardiovascular and photosensitive drug nisoldipine (NIS) has been rationalised. Continuous and monochromatic irradiation of NIS in ethanol obeyed Φ-order kinetics with a sigmoid-shaped quantum yield variation with irradiation wavelength (0.0041–0.35 within 235–390 nm spectral region). Both NIS initial concentration-induced self-photostabilisation effect and the photostabilisation by absorption competitors were quantified (up 70%) and related to a reduction of the photokinetic factor. Finally, the Φ-order kinetics also served to demonstrate the actinometric potential of NIS for the 320–400 nm dynamic range.

Special Section Guest Editorial: Special Section on Fluorescence Molecular Imaging Honoring Prof. Roger Tsien, a Pioneer in Biomedical Optics

Professor Roger Y. Tsien is a renowned world leader in chemical biology and biochemistry whose pioneering work in fluorescence sensing and imaging has revolutionized virtually all of experimental biology. He is an insightful scientist, and a cordial colleague and mentor; always invigorating with his ideas and energy, and inspiring with his vision. His work has profoundly influenced our abilities to study biochemical and molecular processes and events in live cells and animals. His early work on calcium imaging has revealed spatiotemporal characteristics of calcium signaling in various physiological processes and resulted in a widely disseminated use of his methods. But it is his seminal contributions in elucidating the biochemical mechanism of green fluorescent protein (GFP) formation that brought him major acclaim. Over a short period of time, Prof. Tsien further invented a broad spectrum of fluorescent proteins with distinctive colors and characteristics, a technology also adopted in all corners of the biology and biotechnology world. All these contributions have not only provided powerful tools for molecular and cellular imaging, but also advanced our in-depth and systematic understanding of a variety of cellular processes. To date, Prof. Tsien continues to lead and contribute to the emerging fields of molecular and cellular imaging as well as biomedical optics. Because of Prof. Tsien’s seminal scientific achievements, he was awarded the 2008 Nobel Prize in Chemistry for his role in “the green fluorescent protein: discovery, expression and development” and the Wolf Prize in medicine “for his seminal contribution to the design and biological application of novel fluorescent and photolabile molecules to analyze and perturb cell signal transduction.” Prof. Tsien is a member of the National Academy of Sciences and the Institute of Medicine, a Howard Hughes Medical Institute (HHMI) investigator, and a professor at University of California, San Diego.

Exploring Light and Life

Exploring Light and Life

Chemistry and biological applications of photo-labile organic molecules

Photo-labile molecules have been widely used not only in organic synthesis but also in biological study. The chemistry of the typical photo-labile organic molecules, including their structure, mechanism underlying their photo-lability and strategies to integrate them with biomolecules, is reviewed to illustrate the structural basis for photo-activable caged compounds. Biological applications of representative photo-labile caged molecules were also illustrated for a general understanding on the important roles of caged compounds in dynamic biological studies. This tutorial review would provide an interdisciplinary overview on the important area of chemical biological study making use of photo-labile caged compounds.

Photodegradation study of a new activator of the cystic fibrosis chloride channel, the 6‐hydroxy‐10‐chlorobenzo[c]quinolizinium chloride (MPB‐07)

The photodegradation of 6‐hydroxy‐10‐chlorobenzo[c]quinolizinium chloride (MPB‐07), a new activator of the transmembrane conductance regulator chloride channel, was studied in aqueous solutions exposed to artificial daylight (2300 Lux intensity). Various conditions of pH, concentration, and temperature were used. MPB‐07 concentration was determined at regular time intervals by reversed‐phase HPLC. MPB‐07 stability was also studied at pH 7.4 in the dark. Results showed that in all the conditions tested MPB‐07 underwent rapid photodegradation, apparently following first‐order kinetics. Rate constants were dependent on the initial MPB‐07 concentration, temperature, and pH. At pH 7.4, and for concentrations from 1 to 125 μM, half‐lives ranged from 0.681 ± 0.047 to 4.54 ± 0.28 h. The Arrhenius plot was linear and activation energy was calculated to be 20.7 kJ · mol−1. Analysis by chemical ionization‐mass spectrometry showed that the chlorine atom of the MPB‐07 molecule might be replaced by an OH group during the photodegradation process. In the dark, MPB‐07 in solutions at pH 7.4 was found to be stable over a 6‐week period. In conclusion, MPB‐07 is a highly photolabile molecule that should be carefully protected from light when used.

New Concepts in Therapeutic Photomedicine; Photochemistry, Optical Targeting and the Therapeutic Window

Advances in optics technology, synthetic photochemistry, and the science of photobiology make it possible to think beyond phototherapy and photochemotherapy which is dependent on direct photochemical alteration of metabolites or direct phototoxic insult to cells. This report discusses another gender of photomedicine therapy which includes in vivo photoactivation of medicines, photon-dependent drug delivery, and manipulation of host and exposure source to maximize therapeutic index. These therapeutic manipulations are made possible because the skin is highly overperfused and because non-ionizing electromagnetic radiation that enters skin and blood has adequate photon energy to cause electronic excitation. Radiation of 320-800 nm is not very directly phototoxic, is absorbed by a variety of relatively nontoxic photolabile molecules and has an internal dosimetric depth profile. This radiation can therefore be used to activate, deactivate, bind, release or biotransform medications in vivo in skin or other organs. The photochemist, synthetic chemist and photobiologist can collaborate to significantly increase therapeutic possibilities.

Photo-affinity labeling of β-D-xylosidase

As part of a comparative study of the structure and function of a group of glycosidases, we are particularly interested in the properties of a P-Dxylosidase (/3-D-xyloside xylohydrolase, EC 3.2.1.37) induced in Bacillus pumilus [l] . In an attempt to obtain further information on the catalytic site of this enzyme, several potential affinity-labels have been prepared [2-41 and tested on this enzyme. This communication reports on the interaction of a photoaffnity label with the fl-D-xylosidase. The choice of a photolytic activatable ligand is founded on practical considerations, the most important being the easy handling of these products, since the reactive species is formed in situ. The advantage of the aromatic azides, used in this work, over other photolabile molecules (e.g. diazoketones), is their thermal and pH stability. On illumination they produce a highly reactive aryl nitrene, which is thought to be able to react with all amino acid residues. It is concluded that p-azidophenyl xylopyranoside acts on the /3-D-xylosidase as a pseudo photo-affinity label, rather than a true photo-affinity label.

Rapid-flow resonance Raman spectroscopy of photolabile molecules: rhodopsin and isorhodopsin.

We have devised a method for obtaining the resonance Raman spectrum of a photolabile molecule before it is modified by light. The essence of this technique is that the sample is flowed through the light beam at a sufficiently high velocity so that the fraction of photoisomerized (or photodestroyed) molecules in the illuminated volume is very low. This rapid-flow technique has enabled us to measure the resonance Raman spectrum of unphotolyzed bovine rhodopsin in Ammonyx LO detergent solution and in sonicated retinal disc membranes. The major features of these spectra, which are very similar to one another, are the protonated Schiff base line near 1660 cm-1, the ethylenic line at 1545 cm-1, lines due to skeletal modes at 1216, 1240, and 1270 cm-1, and a line due to C-H bending at 971 cm-1. The resonance Raman spectrum of unphotolyzed isorhodopsin formed by the addition of 9-cis-retinal to opsin was also measured. The spectrum of isorhodopsin is more complex and differs markedly from that of rhodopsin. In isorhodopsin, the ethylenic line is shifted to 1550 cm-1, and there are six lines between 1153 and 1318 cm-1. The rapid-flow technique described here makes it feasible to control the extent of interaction between light and any photolabile molecule. We present a theory for predicting the effective sample composition in the illuminated volume as a function of the flow rate, light intensity, and spectral characteristics of the photolabile species.